Display multiplier providing independent pixel resolutions

ABSTRACT

A system, method, and computer program product are provided for a display multiplier. First image data is received for a first display device and second image data is received for a second display device, where the second display device has fewer scan lines than the first display device. A scan line of the second image data is duplicated and a display multiplier output stream is generated that includes a first scan line of the first image data, the scan line of the second image data, a second scan line of the first image data, and the duplicated scan line of the second image data.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Application No.61/768,341, filed Feb. 22, 2013, the entire contents of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to graphics display devices, and moreparticularly to a display multiplier.

BACKGROUND

Conventional graphics processors are limited to two display outputs thatare sufficient for today's phone and tablet applications. However, forsome applications, such as providing displays within an automotiveenvironment more than two display outputs may be needed. For example, asmany as five different displays may exist in an automotive environmentincluding a center dashboard display, a heads-up display (projected ontoa windshield), and two rear seat entertainment displays. Each additionaldisplay output that is provided by a graphics processor increases thepin count of the graphics processor. Increasing the pin count typicallyincreases the cost of the graphics processor. While supporting more thantwo displays is needed for some applications, increasing the pin countmay not be possible for low-cost systems.

Thus, there is a need for addressing this issue and/or other issuesassociated with the prior art.

SUMMARY

A system, method, and computer program product are provided thatimplement a display multiplier. First image data is received for a firstdisplay device and second image data is received for a second displaydevice, where the second display device has fewer scan lines than thefirst display device. A scan line of the second image data is duplicatedand a display multiplier output stream is generated that includes afirst scan line of the first image data, the scan line of the secondimage data, a second scan line of the first image data, and theduplicated scan line of the second image data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a flowchart of a method for generating a displaymultiplier output stream, in accordance with one embodiment;

FIG. 1B illustrates a flowchart of a method for processing the displaymultiplier output stream generated as shown in FIG. 1A, in accordancewith one embodiment;

FIG. 2A illustrates a diagram of a frame including image data for afirst display and image data for a second display, according to oneembodiment;

FIG. 2B illustrates a diagram of the image data for the first display,according to one embodiment;

FIG. 2C illustrates a diagram of the image data for the second display,according to one embodiment;

FIG. 2D illustrates another flowchart of a method for processing thedisplay multiplier output stream generated as shown in FIG. 1A, inaccordance with one embodiment;

FIG. 3 illustrates a diagram of a display controller coupled to adisplay splitter unit, according to one embodiment;

FIG. 4A illustrates the display splitter unit of FIG. 3, according toone embodiment;

FIG. 4B illustrates another display splitter unit of FIG. 3, accordingto one embodiment;

FIG. 5 illustrates another flowchart of a method for generating adisplay multiplier output stream, in accordance with one embodiment;

FIG. 6A illustrates a flowchart of a method for processing the displaymultiplier output stream generated as shown in FIG. 5, in accordancewith one embodiment;

FIG. 6B illustrates a flowchart of a method for processing a serialstream generated as shown in FIG. 6A, in accordance with one embodiment;and

FIG. 7 illustrates an exemplary system in which the various architectureand/or functionality of the various previous embodiments may beimplemented.

DETAILED DESCRIPTION

A graphics processor may be configured to generate a display multiplieroutput stream that includes image data for two or more separate displaydevices for output via a single display connection. A display splitterunit processes the display multiplier output stream to generate aseparate stream of image data and video display signals for each of thetwo or more separate display devices. The display splitter unit includesa pixel buffer for each display device and the pixel buffers are drainedat a pixel output clock rate corresponding to each respective displaydevice.

The pixel output clock rate may be different for each of the separatedisplay devices. Rather than storing several scan lines or an entireframe of image data in each one of the pixel buffers, the rate at whichoriginal scan lines of image data are inserted into the displaymultiplier output stream is reduced by inserting duplicated scan lines.The rate at which the original scan lines for a particular displaydevice are output to the display device is therefore reduced by removingthe duplicated scan lines to display only the original scan lines. Therate at which the original scan lines appear in the display multiplieroutput stream is reduced as needed to substantially match the pixeloutput clock rate for the display device. Therefore, the size of thepixel buffer may be reduced to one or two scan lines.

FIG. 1A illustrates a flowchart of a method 100 for generating a displaymultiplier output stream, in accordance with one embodiment. Atoperation 110, first image data for a first display device is received.In the context of the following description, image data represents acolor associated with a pixel. In one embodiment, a color is encoded asred, green, and blue channels (i.e., RGB) or as luminance andchrominance (i.e., YUV or YCbCr). In the context of the followingdescription a display device may be a conventional CRT (cathode raytube), LCD (liquid crystal display), LED (light emitting diode), plasmadisplay, projected display (e.g., heads up display), or the like. Atoperation 115, second image data for a second display device isreceived, where the second display device has fewer scan lines than thefirst display device. In other words, the height of the second imagedata is less than the height of the first image data.

At operation 120, a scan line of the second image data is duplicated.The scan line that is duplicated may correspond to any one of the scanlines of the second image data. At operation 130, the display multiplieroutput stream is generated. The display multiplier output streamincludes a first scan line of the first image data, the scan line of thesecond image data, a second scan line of the first image data, and theduplicated scan line of the second image data. In one embodiment, thefirst image data and the second image data are interleaved at a scanline granularity. While the scan lines of the first image data arereferred to as the “first” scan line and the “second” scan line, thescan lines may be any one of the scan lines of the first image data. Thefirst scan line is not necessarily the scan line at either the top orthe bottom (depending on the direction in which the scan lines arereferenced) of the first image data, and so forth.

More illustrative information will now be set forth regarding variousoptional architectures and features with which the foregoing frameworkmay or may not be implemented, per the desires of the user. It should bestrongly noted that the following information is set forth forillustrative purposes and should not be construed as limiting in anymanner. Any of the following features may be optionally incorporatedwith or without the exclusion of other features described.

FIG. 1B illustrates a flowchart of a method 130 for processing thedisplay multiplier output stream generated as shown in FIG. 1A, inaccordance with one embodiment. At operation 135, a display multiplieroutput stream is received. The display multiplier output stream mayinclude first image data for a first display device interleaved withsecond image data for a second display device, wherein the second imagedata includes at least one duplicate scan line. At operation 140, scanlines of the first image data are separated from scan lines of thesecond image data to produce separated first image data and separatedsecond image data. At operation 145, the at least one duplicate scanline of the separated second image data is removed to generate retimedsecond image data. At operation 150, the separated first image data isoutput to the first display device. At operation 155, the retimed secondimage data is output to the second display device.

The operations shown in FIG. 1B may be repeated for multiple frames toprovide the frames of the separated first image data to the firstdisplay device and frames of the retimed second image data to the seconddisplay device. The technique used to identify duplicated scan lines forremoval should use the same scheme as used to identify scan lines toduplicate, so that duplicated scan lines are correctly identified. It ispossible for two or more scan lines of the second image data to containthe same data and seem to be duplicated, so comparison of scan lines isnot a robust technique for identifying duplicated scan lines.

FIG. 2A illustrates a diagram of a frame 200 including image data for afirst display and image data for a second display, according to oneembodiment. The frame 200 includes a vertical blanking interval 215 anda horizontal blanking interval 225. The frame 200 may be encoded in adisplay multiplier output stream and then processed to provide a displayA frame 205 to the first display device and a display B frame 207 to thesecond display device. In this manner, a single frame for output by agraphics processor to a display device via a single display connectionmay encode separate image data for display by one or more differentdisplay devices.

Thus, a graphics processor configured to support two display devices viatwo display connections may output two display multiplier output streamsthat each encode image data for two or more different display devices.The two or more different display devices generally are lowerresolutions than the frame 200. For example, one or more of thedifferent display devices may be 720×480 at 60 frames-per-second (fps)compared with 2560×1600 at 60 fps for the frame 200. Therefore, displaysplitting may be a good low cost alternative compared with increasingthe number of pins to support connections for each additional displaydevice. A device or processing unit that is external from a graphicsprocessor that generates the display multiplier output stream may beconfigured to process the display multiplier output stream to split thestream for multiple display devices.

As shown in FIG. 2A, shows the display A frame 205 having an activevideo resolution of W_(A)×H_(A) (W stands for Width and H for Height)and the display B frame 207 having an active video resolution ofW_(B)×H_(B). The combined display resolution of the frame 200 isW_(T)>=W_(A)+W_(B) and H_(T)=max(H_(A), H_(B)). The scan line ratiovalue, a, equals H_(T)/H_(B), where H_(T) is the height of the frame 200less the vertical blanking interval 215. Although the display A frame205 is shown as taller (i.e., H_(A)>H_(B) and display frame A 205 hasmore original scan lines) than the display B frame 207 which hasoriginal and duplicated scan lines, in other embodiments, the display Aframe 205 may be shorter (i.e., having fewer original scan lines) thanthe display B frame 207. Also, in other embodiments, the display A frame205 may not be directly adjacent to the display B frame 207 within theframe 200.

The graphics processor is configured to duplicate scan lines of imagedata for a second display device having a lower height that displays thedisplay B frame 207. Duplicating one or more original scan lines for thedisplay B frame 207 slows that rate at which each new original scan lineis output in the display multiplier output stream. Before the display Bframe 207 is output to the second display device, the duplicated framesare removed to generate retimed image data that including only theoriginal scan lines in the display B frame 207. Each original scan lineof the retimed image data is received by the second display device at alower rate that corresponds to the slower output pixel clock of theshorter display device. The output pixel clock is slower because thenumber of pixels in each frame for the second display device is lessthan the number of pixels in each frame 200.

The second image data included in the display B frame 207 is stored in apixel buffer and drained from the pixel buffer at the output pixel clockrate corresponding to the second display device. Duplicating the scanlines enables the size of the pixel buffer to be minimized because eachscan line of the second image data for the second display device isavailable to be drained from the pixel buffer for display within onescan line of when the scan line of image data will be displayed. Tobetter understand the importance of duplicating the scan lines, consideroutputting the scan line data 220, 221, and 222 without duplication atthe input pixel clock rate corresponding to the frame 200 and the inputpixel clock rate is faster the output pixel clock rate. While the scanline data 220 is output to the second display device, the scan line data221 is written to the pixel buffer, overwriting the scan line data 220.Then, the scan line data 221 is output to the second display devicewhile the scan line data 222 is overwrites the scan line data 221 thatis stored in the pixel buffer. At some point the scan line data beingwritten overwrites scan line data that has not yet been output to thesecond display device. Instead of increasing the capacity of the pixelbuffer to prevent scan line data from being prematurely overwritten, therate at which the scan line data is written to the pixel buffer isreduced by discarding the duplicated scan lines before the pixel bufferis written.

The pixel buffer that stores the first image data may be sized to storeless than a scan line of the display A frame 205 to align the pixeloutput for the second display, where the scan line includes W_(A)pixels. Because the second display device has fewer original scan linescompared with the first display device, the pixel buffer that stores thesecond image data may be sized to store two scan lines of the display Bframe 207, where the scan lines include W_(B) pixels.

As shown in FIG. 2A, scanline data 210 is output for a first scan lineof the display A frame 205, and then the scanline data 220 is output forthe first scan line of the display B frame 207 to generate the displaymultiplier output stream. The scanline data 220 is duplicated for thesecond scan line of the display B frame 207. The scanline data 211 isoutput for a second scan line of the display A frame 205, and then theduplicated scanline data 220 is output for the second scan line of thedisplay B frame 207 to generate the display multiplier output stream.The scanline data 212 is output for a third scan line of the display Aframe 205, and then the scanline data 221 is output for the third scanline of the display B frame 207 to generate the display multiplieroutput stream. The scanline data 221 is duplicated for the fourth andfifth scan lines of the display B frame 207 and the scanline data 222 isoutput for the sixth scan line of the display B frame 207. The scanlinedata 219 is output for the last scan line of the display A frame 205 andthe scanline data 227 is output for the last scan line of the display Bframe 207 to generate the display multiplier output stream. In sum, thescanline data 210, 211, 212, through 219 are included in the displaymultiplier output stream and are interleaved at a scan line granularitywith corresponding scanline data 220, 221, 222, through 227 withduplicated scanline data for one or more scan lines of the seconddisplay device. For example, in one embodiment, the display multiplieroutput stream includes image data in the following order: scanline data210, scanline data 220, scanline data 211, scanline data 220, scanlinedata 212, scanline data 221, etc.

FIG. 2B illustrates a diagram of the image data within the display Aframe 205 for the first display device, according to one embodiment. Thefirst image data for each scan line of the first display device isdrained from the pixel buffer at a pixel clock corresponding to thefirst display device to produce the display A frame 205 on the firstdisplay device. The display A frame 205 is displayed using a verticalblanking interval 226 that equals VBI_(A) and the horizontal blankinginterval 225. The number of scan lines that are output to the firstdisplay device equals H_(A).

FIG. 2C illustrates a diagram of the image data within a retimed displayB frame 208 for the second display, according to one embodiment. Whenthe display multiplier output stream is processed by a display splitterunit, the duplicated scan lines shown in the display B frame 207 for thesecond display device may be discarded and not stored in the pixelbuffer to generate the retimed display B frame 208. The number of scanlines that are output to the second display device equals H_(B). Theretimed display B frame 208 that is the retimed second image data foreach scan line of the second device is drained from the pixel buffer ata pixel clock corresponding to the second display device to produce theretimed display B frame 208 on the second display device. The retimeddisplay B frame 208 is displayed using the vertical blanking interval215 that equals VBI_(B) and the horizontal blanking interval 225.

FIG. 2D illustrates a flowchart of another method 230 for processing thedisplay multiplier output stream generated as shown in FIG. 1A, inaccordance with one embodiment. At operation 235, a display multiplieroutput stream is received. At operation 240, if the end of a scan linefor the first display device is not reached, then at operation 245 aportion of the first image data corresponding to a scan line is storedfor the first display device. The portion may include a single pixel orall of the pixels in a scan line, so it is not necessary to wait for theend of the scan line before storing the portion of the first image data.The end of the scan line may determined based on W_(A) that may beincluded in the display multiplier output stream or may be received as aconfiguration setting. Otherwise, if at operation 240, the end of a scanline for the first display device is reached, then at operation 250, themethod determines if the second image data corresponds to a duplicatedscan line of the second image data. The first image data may correspondto the display A frame 205 and the second image data may correspond tothe display B frame 207.

If the second image data does correspond to a duplicated scan line ofthe first image data, then at operation 265, the method determines ifthe end of a scan line for the second display device is reached. In oneembodiment, portions of the second image data corresponding toduplicated scan lines are discarded and are not stored to generateretimed second image data. Operation 265 is repeated until the end ofthe scan line for the second display device is reached.

If, at operation 250, the second image data does not correspond to aduplicated scan line of the first image data, then at operation 255, aportion of the second image data corresponding to a scan line is storedfor the second display device to generate the retimed second image data,such as the retimed display B frame 208. At operation 260, if the end ofa scan line for the second display device is not reached, then operation255 is repeated. Operation 260 is repeated until the end of the scanline for the second display device is reached. It is not necessary towait for the end of the scan line before storing the portion of thesecond image data. The end of the scan line may determined based onW_(B) that may be included in the display multiplier output stream ormay be received as a configuration setting.

At operation 270, if the end of a frame of the display multiplier outputstream is reached, then the method terminates. Otherwise, at operation245, a portion of the first image data corresponding to a new scan lineis stored for the first display device. The operations shown in FIG. 2Dmay be repeated for multiple frames to provide the frames of the firstimage data to the first display device and frames of the retimed secondimage data to the second display device. The portions of first imagedata and the retimed second image data that are stored in the pixelbuffers for display A and display B, respectively, are output fordisplay by the first display device and the second display device as aseparate process that may operate asynchronously and in parallel withthe storing.

FIG. 3 illustrates a diagram of a display controller 310 coupled to adisplay splitter unit 330, according to one embodiment. Graphicsprocessors, such as the NVIDIA® Tegra® 4 and Tegra® 5 each include twoof the display controllers 310 to provide separate connections to twodisplay devices. As shown in FIG. 3, the display controller 310 isconfigured to combine three separate hardware windows (e.g., windows A,B, and C) with individual memory clients for output to an externaldisplay device. In one embodiment, the maximum resolution of thewindows, when not limited by the memory bandwidth (e.g., 2560×1600 at 60fps), can reach 4096 pixels horizontally and 2160 scan lines vertically.The same resolution applies to the output connection coupled to thedisplay device that has a limit of 2560×1600 @ 60 fps on a displaysignal interface (DSI) (4× lanes) and 1920×1080 @ 60 fps or 4096×2160 @30 fps on a high-definition multimedia interface (HDMI). Note that themaximum resolution may be limited by the respective pixel clock.

As previously explained, the display controller 310 may be configured togenerate a display multiplier output stream that is split by a receivingdevice or unit to generate separate images for display on a display A325 and a display B 335. The combined width of the separate imagesshould not exceed the maximum resolution of the windows and the maximumheight of the images should not exceed the maximum number of scan linesof the windows. The window A buffer fetch 350(0) is configured to readimage data for window A from a memory 305 via a memory controller 320.Similarly, the window B buffer fetch 350(1) and the window C bufferfetch 350(2) are configured to read image data for window B and windowC, respectively, from the memory 305 via the memory controller 320. Acursor unit 354 is configured to read cursor image data from the memory305 via the memory controller 320.

Each of the height scale units 370(0), 370(1), and 370(2) may beconfigured to perform vertical scaling operations that duplicate one ormore scan lines of image data for each respective window. Typically, thefilter units 380(0), 380(1), and 380(2) are configured to filter thescan lines when one or more scan lines are duplicated to improve theimage quality. In one embodiment, a height scale unit 370 and filterunit 380 function as a 2 tap, 16 phase programmable vertical filter. Thevertical filter may have a 16 bit fractional (4.12 bits forposition.fractional portions) accumulator digital differential analyzer(DDA). The 16 bit value is the scan line ratio multiplier, shown as thescan line ratio value a in FIG. 2A (a=H_(T)/H_(B), where H_(T) is theheight of the frame 200 less the vertical blanking interval 215). Theinteger portion selects source scan line(s) of the image data for thewindow, and the fractional portion controls blending between the twosource scan lines, when filtering is enabled. When filtering is notenabled, the integer portion selects one scan line of the image data forthe window and the fractional portion is ignored. As shown in FIG. 3,the filter units 380 may be bypassed and a frame assembly unit 375 mayselect the scaled image data output by one or more of the height scaleunits 370 instead of selecting a corresponding filtered image dataoutput by one or more of the filter units 380 to generate an outputstream.

When the display controller 310 is configured to generate a displaymultiplier output stream, the filtering should be disabled so that scanlines of the image data for the window may be duplicated, but blendingwill not be performed to modify the image data for each of the originalor duplicated scan lines. The height scale units 370 are configured toduplicate one or more scan lines of image data for a particular windowso that each scan line is within one scan line of the timing for thecorresponding display device. In other words, spatial (vertical) lineduplication is used to provide temporal proximity for the display deviceand reduce the amount of memory needed to store the image data in thedisplay splitter unit 330, as further described in conjunction withFIGS. 4A and 4B. The width of the target display device should be equalto the width of the window to be displayed in order to preserve originalpixel values (i.e. so there is no loss of image quality).

The frame assembly unit 375 is typically configured to generate anoutput stream for display by a single display device, where one of thewindows A, B, or C corresponds to a “desktop” image, and the remainingwindows are overlayed on the desktop image along with the cursor. Whenthe frame assembly unit 375 is configured to generate a displaymultiplier output stream two or more of the windows A, B, or C maycorrespond to different display devices, so that the image data for thewindows are not necessarily overlaid, but are instead positioned toproduce frames of combined image data, such as the frame 200 shown inFIG. 2A. The separate image data for each of the display devices maythen be split by a display splitter unit 330 for display on each of theseparate display devices, a display A 325 and a display B 335. In otherembodiments, the number of window buffer fetch units 350, height scaleunits 370, and filter units 380 is increased to support additionaldisplay devices. In another embodiment, the number of window bufferfetch units 350, height scale units 370, and filter units 380 isdecreased to two to support two display devices. As previouslyexplained, a processor may include more than one display controller 310that can each be configured to generate a display multiplier outputstream.

FIG. 4A illustrates the display splitter unit 330 of FIG. 3, accordingto one embodiment. The display splitter unit 330 is a simplified blockdiagram that illustrates the processing units used to perform thedisplay splitting operations and the display splitter unit 330 may beincluded within a device or may be a discrete device. In someembodiments, additional processing units and/or circuitry may beincluded in the display splitter unit 330. The display splitter unit 330includes circuitry in three different clock domains, an input clockdomain 402 associated with the display controller 310, a display A clockdomain 422 associated with the display A 325, and a display B clockdomain 424 associated with the display B 335.

A format decode unit 405 receives the display multiplier output streamthat includes image data for two different display devices and splitsthe display multiplier output stream into scan lines of first image datafor the display A 325 and scan lines of second image data for thedisplay B 335. The first image data may correspond to the display Aframe 205 shown in FIG. 2B and the second image data may correspond tothe display B frame 207 shown in FIG. 2C.

A line selection unit 410-A receives the scan lines of the first imagedata and determines which scan lines to pass through to a scan linebuffer 415-A. When none of the scan lines are duplicate scan lines, allof the scan lines are passed through to the scan line buffer 415-A.Otherwise, the duplicate scan lines are discarded by the line selectionunit 410-A so that the duplicate scan lines do not reach the scan linebuffer 415-A. Similarly, a line selection unit 410-B receives the scanlines of the second image data and determines which scan lines to passthrough to a scan line buffer 415-B. When none of the scan lines areduplicate scan lines, all of the scan lines are passed through to thescan line buffer 415-B. Otherwise, the duplicate scan lines arediscarded by the line selection unit 410-B so that the duplicate scanlines do not reach the scan line buffer 415-B. The line selection units410 generate retimed image data when one or more duplicate scan linesare removed.

In one embodiment, the line selection units 410 may also be configuredto discard pixels of a scan line based on the width of the respectivedisplay device. The line selection units 410 may be configured toimplement the same DDA algorithm as the height scale unit 370 and filterunit 380. Specifically, the DDA accumulator and the fixed integer scanline ratio multiplier (4 bits+12 bits fractional) may be implemented, sothat the duplicated scan lines may be correctly identified by the lineselection units 410.

The scan line buffers 415 may be implemented as a pixelfirst-in-first-out buffer (FIFO) having an input clock (e.g., HDMI inputpixel clock) that may operate at a higher speed compared with an outputclock that corresponds to a pixel clock of a display device. Each of thescan line buffers 415 may be sized to store at least one scan line for adisplay device (e.g., 24 bit/pixel). A phase-locked loop (PLL) 425-Agenerates a clock signal for the display A clock domain 422 and a PLL425-B generates a clock signal for the display B clock domain 424. ThePLLs 425 and video format units 420 receive control input signals fromthe format decode unit 405. Specifically, the video format units 420receive a VSYNC signal and the PLLs 425 receive the input pixel clock.

The video format units 420 each reads pixels from the respective scanline buffer 415 and output them according to the output format neededfor each display device. The active video of each display device shouldbe properly aligned by the video format units 420 to ensure that thereis no starvation or overflow of the scan line buffers 415. In oneembodiment, a VSYNC to VSYNC out delta value is provided (in number oflines) by each video format unit 420 to properly align the first activeline of each display device. The actual VBI from the input stream shouldbe greater in time than the maximum VBI of each of the display devices.For example, as shown in FIG. 2A, the duration in time of VBI_(T) isgreater than the duration in time of either VBI_(A) or VBI_(B). In oneembodiment, the display device having fewer active scan lines (i.e., theshortest height) may be coupled to the video format unit 420-B and theline selection unit 410-A may be removed.

FIG. 4B illustrates another display splitter unit 330 of FIG. 3,according to one embodiment. The display splitter unit 330 shown in FIG.4B includes a serializer unit 400 that is coupled to a de-serializerunit 430 by a serial link 450. The serial link 450 may be implemented asautomotive pixel link (APIX), DSI, CSI-2, FPD-Link, or the like. Theserializer unit 400 and the de-serializer unit 430 may be implementedwithin separate discrete devices that are located a short distance apartor several feet apart. The serializer unit 400 and de-serializer unit430 are simplified block diagrams that illustrate the processing unitsused to perform the display splitting operations. In some embodiments,additional processing units and/or circuitry may be included in theserializer unit 400 and/or de-serializer unit 430.

The format decode unit 431, and line selection units 435 performsubstantially the same operations as the previously described formatdecode unit 405 and line selection units 410. A digital multiplexer 445is configured to combine the image data for the display A 325 and thedisplay B 335 after any duplicate scan lines are removed and transmitthe image data for the display A 325 and the display B 335 over theserial link 450 on different virtual channels. The combined image datais stored in a scan line buffer 442 before being transmitted on theserial ink 450. The scan line buffer 442 may be implemented as a pixelFIFO having an input clock (e.g., HDMI input pixel clock) that mayoperate at a higher speed compared with an output clock that correspondsto the serial link 450. The input clock domain 432 corresponds to theinput clock and a serial link clock domain 452 corresponds to the seriallink 450.

The de-serializer unit 430 receives the combined image data that istransmitted over the serial ink 450. A digital demultiplexer 455 isconfigured to output the image data received over a first virtualchannel to a scan line buffer 460-A and output the image data receivedover a second virtual channel to a scan line buffer 460-B. The scan linebuffers 460 may be implemented as pixel FIFOs having an input clock thatmay operate at a different speed compared with an output clock thatcorresponds to the respective display A 325 or the display B 335. Theserial link clock domain 452 corresponds to the serial link 450, adisplay A clock domain 462 corresponds to the display A 325, and adisplay B clock domain 464 corresponds to the display B 335. Videoformat units 465 and PLLs 475 perform substantially the same operationsas previously described video format units 420 and PLLs 425,respectively.

In an embodiment in which the display B 335 includes a frame buffer, theoutput clock may be the same as the input clock (i.e., serial link clockdomain 452 and display B clock domain 464 may be a single clock domain)and the resulting vertical blanking interval and horizontal blankinginterval for the display B 335 are much larger than when the outputclock is different than the serial link clock. Using the same pixelclock eliminates the need for the PLL 475-B in the de-serializer unit430. In one embodiment, the line selection unit for the display devicehaving the greatest number of active scan lines (i.e., the tallestheight) may be removed. In other words, when the display B 335 has feweractive scan lines than display A 325, the line selection unit 435-A canbe omitted from the serializer unit 400, reducing the implementationcost of the serializer unit 400.

FIG. 5 illustrates another flowchart of a method 500 for generating adisplay multiplier output stream, in accordance with one embodiment. Atoperation 510, first image data for a first display device is receivedby a display controller 310. At operation 515, second image data for asecond display device is received by the display controller 310, wherethe second display device has fewer scan lines than the first displaydevice.

At operation 520, a scan line ratio multiplier value is computed by thedisplay controller 310. The scan line ratio multiplier value is used toduplicate one or more scan lines of the second image data. Filtering isdisabled for the scaling operation that duplicates the one or more scanlines. At operation 530, the display multiplier output stream isgenerated. The display multiplier output stream includes scan lines ofthe first image data that are interleaved with corresponding scan linesand the duplicated scan lines of the second image data.

FIG. 6A illustrates a flowchart of a method 600 for processing thedisplay multiplier output stream generated as shown in FIG. 5, inaccordance with one embodiment. The display multiplier output stream maybe processed by a serializer unit 400 of a display splitter unit 330 asshown in FIG. 4B. At operation 635, the display multiplier output streamis received by the serializer unit 400. At operation 640, if the end ofa scan line for the first display device is not reached, then atoperation 645, a portion (e.g., at least one pixel) of the first imagedata corresponding to a scan line for the first display device istransmitted over the serial link 450, so it is not necessary to wait forthe end of the scan line before transmitting the portion of the firstimage data. Otherwise, if at operation 640, the end of a scan line forthe first display device is reached, then at operation 650, theserializer unit 400 determines if the second image data corresponds to aduplicated scan line of the second image data. The end of the scan linemay determined based on W_(A) that may be included in the displaymultiplier output stream or may be received as a configuration setting.

If the second image data does correspond to a duplicated scan line ofthe second image data, then at operation 665, the serializer unit 400determines if the end of a scan line for the second display device isreached. Operation 665 is repeated until the end of the scan line forthe second display device is reached. The duplicated scan line isdiscarded and is neither stored nor transmitted by the serializer unit400.

If, at operation 650, the second image data does not correspond to aduplicated scan line of the second image data, then, at operation 655, aportion of the second image data corresponding to a scan line for thesecond display device is transmitted over the serial link 450 togenerate retimed second image data, so it is not necessary to wait forthe end of the scan line before transmitting the portion of the secondimage data. At operation 660, if the end of a scan line for the seconddisplay device is not reached, then operation 655 is repeated. Operation660 is repeated until the end of the scan line for the second displaydevice is reached. The end of the scan line may determined based onW_(B) that may be included in the display multiplier output stream ormay be received as a configuration setting.

At operation 670, if the end of a frame of the display multiplier outputstream is reached, then serializer unit 400 terminates processing.Otherwise, at operation 645, a portion of the first image datacorresponding to a new scan line for the first display device istransmitted over the serial link 450. The operations shown in FIG. 6Amay be repeated by the serializer unit 400 for multiple frames toprovide the frames of the first image data to the first display deviceand frames of the retimed second image data to the second displaydevice.

FIG. 6B illustrates a flowchart of a method 610 for processing a serialstream generated as shown in FIG. 6A, in accordance with one embodiment.The serial stream may be transmitted over the serial link 450 to thede-serializer unit 430. At operation 605, the serial stream is receivedby the de-serializer unit 430. The serial stream may include two of morevirtual channels over which first image data for a first display isinterleaved with retimed second image data for a second display device.

At operation 615, the de-serializer unit 430 determines if the imagedata received via the serial link 450 is for the display A channel, and,if so, at operation 620, a portion of the first image data correspondingto a scan line is stored for the first display device (i.e., display A325). Otherwise, at operation 625, de-serializer unit 430 stores aportion of the retimed second image data for the second display device(i.e., display B 335). At operation 630, if the end of a frame of thedisplay multiplier output stream is reached, then the de-serializer unit430 terminates processing. Otherwise, the de-serializer unit 430 returnsto operation 615. The operations shown in FIG. 6B may be repeated by thede-serializer unit 430 for multiple frames to provide the frames of thefirst image data to the first display device and frames of the retimedsecond image data to the second display device.

The portions of first image data and the retimed second image data thatare stored may be output for display by the first display device and thesecond display device, respectively, as a separate process that mayoperate asynchronously and in parallel with the storing.

FIG. 7 illustrates an exemplary system 700 in which the variousarchitecture and/or functionality of the various previous embodimentsmay be implemented. As shown, a system 700 is provided including atleast one central processor 701 that is connected to a communication bus702. The communication bus 702 may be implemented using any suitableprotocol, such as PCI (Peripheral Component Interconnect), PCI-Express,AGP (Accelerated Graphics Port), HyperTransport, or any other bus orpoint-to-point communication protocol(s). The system 700 also includes amain memory 704. Control logic (software) and data are stored in themain memory 704 which may take the form of random access memory (RAM).

The system 700 also includes input devices 712, a graphics processor706, one or more display splitter units 330, and one or more displaydevices 708. User input may be received from the input devices 712,e.g., keyboard, mouse, touchpad, microphone, and the like. In oneembodiment, the graphics processor 706 may include a plurality of shadermodules, a rasterization module, etc. Each of the foregoing modules mayeven be situated on a single semiconductor platform to form a graphicsprocessing unit (GPU). The graphics processor 706 may also include oneor more display controllers 310 that are each coupled to a displaysplitter unit 330.

In the present description, a single semiconductor platform may refer toa sole unitary semiconductor-based integrated circuit or chip. It shouldbe noted that the term single semiconductor platform may also refer tomulti-chip modules with increased connectivity which simulate on-chipoperation, and make substantial improvements over utilizing aconventional central processing unit (CPU) and bus implementation. Ofcourse, the various modules may also be situated separately or invarious combinations of semiconductor platforms per the desires of theuser.

The system 700 may also include a secondary storage 710. The secondarystorage 710 includes, for example, a hard disk drive and/or a removablestorage drive, representing a floppy disk drive, a magnetic tape drive,a compact disk drive, digital versatile disk (DVD) drive, recordingdevice, universal serial bus (USB) flash memory. The removable storagedrive reads from and/or writes to a removable storage unit in awell-known manner.

Computer programs, or computer control logic algorithms, may be storedin the main memory 704 and/or the secondary storage 710. Such computerprograms, when executed, enable the system 700 to perform variousfunctions. For example, a compiler program that is configured toexaminer a shader program and enable or disable attribute buffercombining may be stored in the main memory 704. The compiler program maybe executed by the central processor 701 or the graphics processor 706.The main memory 704, the storage 710, and/or any other storage arepossible examples of computer-readable media.

In one embodiment, the architecture and/or functionality of the variousprevious figures may be implemented in the context of the centralprocessor 701, the graphics processor 706, an integrated circuit (notshown) that is capable of at least a portion of the capabilities of boththe central processor 701 and the graphics processor 706, a chipset(i.e., a group of integrated circuits designed to work and sold as aunit for performing related functions, etc.), and/or any otherintegrated circuit for that matter.

Still yet, the architecture and/or functionality of the various previousfigures may be implemented in the context of a general computer system,a circuit board system, a game console system dedicated forentertainment purposes, an application-specific system, and/or any otherdesired system. For example, the system 700 may take the form of adesktop computer, laptop computer, server, workstation, game consoles,embedded system, and/or any other type of logic. Still yet, the system700 may take the form of various other devices including, but notlimited to a personal digital assistant (PDA) device, a mobile phonedevice, a television, etc.

Further, while not shown, the system 700 may be coupled to a network(e.g., a telecommunications network, local area network (LAN), wirelessnetwork, wide area network (WAN) such as the Internet, peer-to-peernetwork, cable network, or the like) for communication purposes.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A method, comprising: receiving first image datafor a first display device; receiving second image data for a seconddisplay device, wherein the second display device has fewer scan linesthan the first display device; computing a scan line ratio multipliervalue as a height in scan lines of a frame including the first imagedata and the second image data divided by a height in scan lines of thesecond display device; duplicating a scan line of the second image dataa number of times based on the scan line ratio multiplier value; andgenerating a display multiplier output stream that includes a first scanline of the first image data, the scan line of the second image data, asecond scan line of the first image data, and the duplicated scan lineof the second image data.
 2. The method of claim 1, wherein the firstimage data and the second image data are interleaved at a scan linegranularity.
 3. The method of claim 1, further comprising disablingfiltering of the second image data.
 4. The method of claim 1, whereinthe first image data and the second image data are combined within aframe having a height that is equal to or greater than a number of scanlines of the first display device and a width that is equal to orgreater than a sum of a width of the first display device and a width ofthe second display device.
 5. A method, comprising: receiving firstimage data for a first display device; receiving second image data for asecond display device, wherein the second display device has fewer scanlines than the first display device; duplicating a scan line of thesecond image data; and generating, by a first device, a displaymultiplier output stream that includes a first scan line of the firstimage data, the scan line of the second image data, a second scan lineof the first image data, and the duplicated scan line of the secondimage data, wherein a second device is configured to: receive thedisplay multiplier output stream; separate scan lines of the first imagedata from scan lines of the second image data; remove the duplicate scanline of the separated second image data to generate retimed second imagedata; output the separated first image data to the first display device;and output the retimed second image data to the second display device.6. The method of claim 5, the second device further configured to, priorto outputting the separated first image data, store a portion of theseparated first image data in a scan line buffer configured to store onescan line of pixels for the first display device.
 7. The method of claim6, wherein the portion of the separated first image data is written tothe scan line buffer using a first clock that corresponds to the displaymultiplier output stream, and further comprising reading the portion ofthe separated first image data from the scan line buffer using a secondclock that corresponds to the first display device.
 8. The method ofclaim 5, the second device further configured to, prior to outputtingthe retimed second image data, store a portion of the retimed secondimage data in a scan line buffer configured to store one scan line ofpixels for the second display device.
 9. The method of claim 8, whereinthe portion of the retimed second image data is written to the scan linebuffer using a first clock that corresponds to the display multiplieroutput stream, and further comprising reading the portion of the retimedsecond image data from the scan line buffer using a second clock thatcorresponds to the second display device.
 10. The method of claim 9,wherein a number of the at least one duplicate scan line of theseparated second image data that is removed is based on the scan lineratio multiplier value.
 11. The method of claim 5, the second devicefurther configured to compute a scan line ratio multiplier value as aheight in scan lines of a frame including the first image data and thesecond image data divided by a height in scan lines of the seconddisplay device.
 12. A system, comprising: a memory configured to storefirst image data for a first display device and second image data for asecond display device; and a display controller that is coupled to thememory and configured to: receive the first image data for the firstdisplay device; receive the second image data for the second displaydevice, wherein the second display device has fewer scan lines than thefirst display device; compute a scan line ratio multiplier value as aheight in scan lines of a frame including the first image data and thesecond image data divided by a height in scan lines of the seconddisplay device; duplicate a scan line of the second image data a numberof times based on the scan line ratio multiplier value; and generate adisplay multiplier output stream that includes a first scan line of thefirst image data, the scan line of the second image data, a second scanline of the first image data, and the duplicated scan line of the secondimage data.
 13. The system of claim 12, wherein the first image data andthe second image data are interleaved at a scan line granularity. 14.The system of claim 12, wherein the display controller is furtherconfigured to disable filtering of the second image data.
 15. The systemof claim 12, wherein the first image data and the second image data arecombined within a frame having a height that is equal to or greater thana number of scan lines of the first display device and a width that isequal to or greater than a sum of a width of the first display deviceand a width of the second display device.
 16. A system, comprising: adisplay controller configured to generate a display multiplier outputstream including first image data for a first display device interleavedwith second image data for a second display device, wherein the secondimage data includes at least one duplicate scan line; and a displaysplitter unit that is coupled to the display controller and configuredto: receive the display multiplier output stream; separate scan lines ofthe first image data from scan lines of the second image data; removethe at least one duplicate scan line of the second image data togenerate retimed second image data; output the separated first imagedata to the first display device; and output the retimed second imagedata to the second display device.